Generally, three drives are superimposed on the generated surface of a distributing roller in inking or damping units of offset printing presses. First there is the positive drive of the distributing roller by a transmission, more particularly a geared transmission, which is responsible for the rotation of the distributing roller, second there is the positive drive for lateral reciprocation of the roller and third there is the friction drive produced by the pressure with which the distributing roller cooperates with contiguous rollers.
A drive such as described above is generally disclosed in DD-PS 41 474 and according to this disclosure the drive has a loose gear which transmits the lateral reciprocation to the distributing roller and this loose gear has two teeth less than the gear which transmits rotation to the distributing roller, the latter gear being rigidly connected to a bearing extension of the distributing roller. The loose gearwheel is connected by a pin with a roller to a circular cam groove in a sleeve, which is rigidly connected to the bearing extension, the pin being disposed in the hub of the loose gear. When the loose gear having two teeth less than the other gear rotates, the pin and roller in the hub are driven with acceleration circularly in the cam groove, resulting in the sleeve with the bearing extension and, therefore, the distributing roller being reciprocated once by the distance of the pitch of the cam groove relative to the number of teeth of the loose gear and of the rotation-transmitting gear.
When the pin with the roller experiences accelerated circular engagement with respect to the cam groove, the loose gear experiences vibrations emanating from the press, for example, from the drive gear train of the printing cylinder and/or from the friction drive of the rollers and cylinder with the rotary vibrations and/or distributing vibrations deriving from the plate cylinder recess as the inking rollers run on and off and due to the possibility of the inking rollers being driven with peripheral slip. Also, the loose gear experiences vibrations arising from the derivation of the cyclic traversing movement of the distributing roller from a rotary movement of the cam groove with the roller entrained therein with acceleration in the circular groove, the roller being rigidly connected by way of the pin to the hub of the loose gear.
The loose gear is relatively light in weight and so its moment of inertia is inadequate to damp the vibrations which are superimposed on one another. Additionally, since the loose gear is rigidly connected to a gear of the drive gear train from the printing unit rollers, the vibrations of the loose gear are transmitted without damping as far as the printing rollers. Thus, this kind of drive entails a risk of the formation of gear tooth striping on the print support, as a result of play between tooth flanks due to the undamped vibrations of the loose gear.